Hydro-Slotting Perforation (HSP)

Stage 1.Perforating System Referencing

Hydro-Slotting Perforation (HSP) is an advanced technology where tubing is used to run a cutting tool into the well. Geophysical methods, including gamma-ray logging, ensure precise alignment of the cutting tool at the specified well interval.

A marker joint is then securely positioned at the predetermined interval. If needed, slotting can be oriented along a specific azimuth for optimal perforation results.

Stage 2.Casing Perforation

HSP involves a team specializing in major workover or well servicing operations using standard flushing equipment and a pumping unit (e.g., TsA-320, SIN-35, or similar units) capable of generating and maintaining pressures up to 15 MPa for extended periods of 8 to 10 hours.

At the wellhead, the pumping unit creates initial pressure of 1.5–2 MPa, allowing the cutting tool to move into the working position. The cutting discs then rest against the inside of the casing.

As the tubing and cutting tool reciprocate within the target interval, increasing pressure within the tubing line gradually pushes the cutting discs through the casing walls. This process creates longitudinal slots, spaced 180 degrees apart, through plastic deformation of the casing metal. Deformation is closely monitored using a weight indicator to ensure precise and consistent formation of the slots.

Stage 3. Cavern Formation

Once the slots are formed, the next step is high-pressure water jet treatment. Nozzle jets, operating at up to 15 MPa, are used to wash away the cement sheath and surrounding rock formations, creating filtration channels and caverns in the near-wellbore zone to improve fluid inflow to the well.

These nozzles target the newly created slots, working in short bursts (3–5 minutes) at each point. This localized treatment achieves a washout resolution of 200–300 mm, forming effective channels that significantly enhance the fluid inflow to the well.

Well Casing Cut by a Slotting  
Perforation Tool on a Bench

External View

The total perforation area achieved is 0.024 m² per linear meter of casing. This area is equivalent to the perforations made by 34 shaped charges, each producing a 30 mm diameter hole.

The surrounding casing material remains stable due to uniform stress relief, preventing the slots from closing. Total perforation length per single RIH-ROOH operation is up to 50 meters.

Internal View

The slots can be oriented azimuthally,

with the possibility of creating 2 or 4 slots per linear meter of the well length.

The edges of the slots are milled by the ribbed surfaces of the cutting discs, leaving them free of burrs.

To test the performance of the hydraulic nozzles of the slotting tool, a concrete block made from durable cement grade 400 was cured for one month under optimal conditions.

The tests were carried out with a liquid pressure of 15 MPa,

with the nozzles operating for 2 minutes.

This resulted in the formation of a cavern with a depth of 0.66 meters.

Shaped-Charge Jet Perforation Result

Hydro-Slotting Perforation Result

Quality Control – CAT Method

The well survey data from a seisviewer was interpreted to monitor the quality of the resulting HSP intervals. An embossed model was generated to visualize the results.

The HSP results were then compared with those of previous shaped-charge jet perforation operations, which showed several perforations of poor quality, as well as localized swellings.

Shaped-Charge Jet Perforation (SCJP)

Shaped-charge jet perforation has been used globally for over 60 years. However, despite its long-standing application, it has resents several key disadvantages:

• Destructive impact on the cement sheath.
• Lack of a centering system, leading to inconsistent hole quality.
• Unreliable detonation of some shaped charges.
• Formation of glass in terrigenous rocks, causing near-wellbore zone colmatation.
• Limited number of fluid inflow channels and drainage zones involved due to poor quality of perforation holes.

Hydro-Slotting Perforation (HSP)

Hydro-slotting perforation addresses the disadvantages of the jet perforation, offering several significant benefits:

• Safe technology.
• No damage to the cement sheath.
• Creation of large perforation zones and large caverns.
• Optimal connection between the well and formation.
• Enhanced production and increased oil recovery achieved in further operations.

Accident-Free Hydraulic Fracturing

When used prior to hydraulic fracturing, HSP ensures reliable hydrodynamic connectivity between the well and formation, offering multiple benefits:

• Significant reduction in hydraulic resistance during proppant injection at the well/formation interface.
• Elimination of emergency interruptions caused by perforation issues during proppant injection.
• Capability to handle coarse proppant fractions.
• Capability to handle high proppant concentrations.
• Accommodation of high proppant pumping speeds.
• Applicability in both horizontal and shallow wells.
• Facilitation of selective hydraulic fracturing after squeeze cementing.
• Support for oriented hydraulic fracturing, allowing slot orientation along a specified azimuth aligned with formation stress distribution.

The Most Reliable Solution

HSP is increasingly deployed in both production and injection wells, particularly before hydraulic fracturing. In many well, HSP resulted in free-flowing hydrocarbon production.  HSP reperforation often provides flow rates restoring to original levels. As a preparation to hydraulic fracturing, HSP leads to increased well injectivity and reduced fracturing pressure requirements.

These benefits have been documented in expert reviews and positive feedback from leading oil companies that have successfully implemented the HSP technology.